Gammadot Rheology Testing & Consultancy Services
Unit 5C, Leaton Industrial Estate, Bomere Heath. Shrewsbury. Shropshire. SY4 3AP. UK
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  Gammadot Rheology Bi-Annual Newsletter - September 2017

Brand New Porpoise P9 Capillary Rheometer Commissioned

Gammadot Rheology has recently commissioned a brand new state of the art twin bore capillary rheometer supplied by Molecular Control Systems Ltd.

The P9 IntelliRheo™ is one of the most technically advanced laboratory capillary rheometers for the determination of the flow behavior of a wide range of materials with all the benefits of a twin bore system. The computer controlled instrument offers testing abilities to measure shear viscosity, extensional viscosity, wall slip, melt fracture and rupture with a variety of dies and accessories.

The IntelliRheo™ software offers standard test control functionalities as well as scientific evaluation capabilities for a better understanding of the data. Its ergonomic design allows easy access and experimentation.


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FOCUS ON: Oscillatory Rheometry & Quality Control

The controlling factor in all polymer conversion processes is the material's rheological behaviour - if you can't deform & make the material flow, you can't process it! The rheological response of a polymer melt is also highly sensitive to material structure. A rotational rheometer in oscillation mode (Oscillatory Rheometry), can detect discrete changes in structural properties, therefore affording a precise & accurate method of providing quality control for all aspects of the process. Whether it be screening incoming raw materials to discriminate batch to batch variance, optimising the conversion process through minimising the effects of thermal & shear history, or determining the cause of degradation in failed components, oscillatory rheometry can provide this information in a fast & reproducible manner.

As mentioned, Oscillatory rheometry measurements are made utilising a rotational rheometer. This type of rheometer is an extremely sensitive, yet robust bench top instrument which is available in a number of machine configurations. The measurement system of the instrument is modular and therefore a wide range of test parameters can be derived in conjunction with the use of either plate / plate, cone & plate or coaxial cylinder systems.
Mainstay of Gammadot's rotational rheometry services - the Reologica ViscoTech high resolution rotational rheometer upgraded to StressTech  HR specifications.

Some examples of the type data that can be produced on the instrument and their applications are demonstrated below:

Simple 'Go / No Go' quality control programmes
Quality control program based on a 'go / no go' process window derived from characterising 'good' & 'bad' samples
Controlling quality of incoming batches of material is critical to maintaining an optimised conversion process and minimising reject rates. The graph on the left demonstrates a simple 'Go / No Go' quality control programme set up for an automotive components moulder who operated a 'just in time' manufacturing regime. The company had been experiencing problems with variation in the properties of supplied batches of Polypropylene, evident in fluctuating levels of product reject rates - which threatened planned delivery schedules. By characterising samples taken from 'Good' & 'Bad' batches of material a simple 'process window' (the limits of which are indicated by the green curves on the graph), was compiled against which future batches could be compared - enabling any incoming materials that fell outside of the window to be rejected before entering the production line.

Application of Rheology to Failure Analysis
Another major application of oscillatory rheometry is the support of failure analysis projects. The slide on the right displays data produced as part of one such project, carried out for an electrical connectors manufacturer. Problems arose with a particular product which had a brass fitting pressed into a central boss within the moulding. This product was sourced from two different manufacturing facilities - one in Bulgaria which produced mouldings with no problems and one in Poland which was producing components that cracked upon pressing the brass insert into position. The connector was moulded out of a glass-filled PolyButylene Terephthalate (PBT) grade, a semi-crystalline, hygroscopic (moisture sensitive) material. Sections removed from both 'good' and failed components were rheologically characterised and it could be seen there was almost a full (log) decade drop in complex viscosity across the measured frequency range between the samples. This considerable decrease indicated there had been a sharp reduction in molecular weight due to degradation - chain scission probably being a result of inadequate pre-process drying.
Rheology used to determine the most likely causes of component failure
To confirm this theory, test specimens were injection moulded after zero, one, two & three hours drying in a vacuum oven @ a temperature of 135°C. Sections of the dried mouldings and virgin granules were measured and it could be seen that the viscosity response of the undried (zero hours) moulding lays closest to the failed sample's viscosity curve. As predicted, as drying time was increased the level of degradation decreased demonstrated by an increased retention of properties. At the optimised drying time for PBT of 3 hours @ 135°C it could be seen the viscosity had risen to a level comparable to that of the 'good' sample although interestingly, after only one hours drying, properties increased to a similar level.

Cure Kinetics of Thermosetting Materials
Accurate measurement of cure kinetics for thermosetting plastics

Due to the modular nature of the rotational rheometer measurement system, disposable plate / plate systems can be used to perform tests on curing and/or corrosive materials. Measurements are usually carried out either isothermally at fixed strain & frequency as a function time (Isothermal cure), or fixed strain & frequency as a function of temperature, (reactive viscosity measurements). The plot to the left depicts the viscosity responses of an NBR rubber compound as a function of different heating rates, at 3 different frequencies. Running as a function of temperature in cooling mode is also excellent at determining phase transitions in hot melt adhesives and investigating the effect of changing ingredient ratios in compound trials.

Control software for modern rotational rheometers are exceptionally versatile. A useful function of software is the ability to 'string' individual test programmes into a project 'macro'. The graph on the right is an example of this. A manufacturer of products for the offshore oil industry was encapsulating components in a large volume of Polyurethane, for use in offshore applications. The cured resin was required to reach a specific modulus to ensure integrity of the moulding at the pressures experienced in deep sea conditions. Full cure of the moulding was not reached until almost 24 hours after mixing and casting, and the cure kinetics passed through three distinct phases: an initial exothermic reaction which raised the temperature of the casting from 20°C to 130°C, an hour at a constant 130°C (a result of adiabatic heating), followed by an 18 hour slow cooling phase.

This was easily replicated by using three test templates joined together in a project macro. All templates used the same fixed frequency & strain amplitude with the first programme running a heating ramp from 20°C to 130°C @ a heating rate of 20°C/min (to replicate the heat generated during the initial exothermic reaction). The second programme was an isothermal measurement @ 130°C for one hour, (simulating adiabatic heating conditions), and the third programme an extremely slow cooling ramp from 130°C to 20°C over 18 hours (-0.102°C/min).
Multi-test programme to accurately simulate a large volume curing process

In addition to the small cross section of test programmes highlighted above, the instrument is able to determine: thermal degradation through melt stability studies, yield stress analysis, creep / creep recovery and other standard rheology / viscometry techniques, making the rotational rheometer an intrinsic part of a modern day laboratories characterisation suite. Hopefully this short piece has given an insight into the value of utilising controlled stress rheometry in the solution of a variety of quality control issues affecting processing, ranging from pre-process discrimination of raw material to determining likely cause of failure in failed products. Why don't you give Gammadot Rheology a call and discuss your quality control needs today?

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Key Gammadot Test Services

Melt Flow Rate
Rotational Rheometry


Melt Flow Rate (Index) / Melt Volume Rate - MFR (MFI) / MVR to ISO standard 1133 or ASTM D1238. Full suite of weights and both standard and half sized capillary dies.
Rotational Rheometry - Shear viscosity versus shear rate / Time / Temperature • Oscillatory Rheometry as a function of Frequency / Time / Temperature • Cure Kinetics / Melt Stability / Thermal Degradation Studies to ASTM standard D4440.

ODR Rubber Rheometry
Capillary Rheometry


Rubber Cure Rheometry - With uprated temperature control and datalogging system. Cure Kinetics to ISO standard 3417 or ASTM 2084.
Capillary Rheometry - Shear viscosity as a function of shear rate • Extensional viscosity as a function of extension rate • Melt Density to ISO standard 11443 or ASTM D3835.

P.v.T. Behaviour
Brookfield Viscometry


High Pressure Dilatometry (PvT Behaviour) - Specific Volume or Density as a function of temperature & pressure.
Brookfield Viscometry - LV & RV viscometer ranges available • Full range of RV / LV spindles plus Small Sample Adaptor (SSA) • UL Adaptor for accurate low viscosity measurements.

Check out our other testing services too - A variety of thermal & mechanical testing methods are available on request. Also, further savings can be made with volume test discounts: 6 - 10 tests = 10% discount, 11 to 15 tests = 15% discount & 16+ tests = 25% discount!

Finally, don't forget our one-stop material characterisation for flow simulation services - providing a complete profile of material data for Autodesk Moldflow, Moldex 3D & Sigmasoft 3D simulation software packages - Thermoplastic, Thermoset & Elastomer.
Independent Polymer Technology Ltd - Premier testing, consultancy & analysis laboratory providing services covering all aspects of polymer technology Artis Ltd - UK's Leading Rubber Testing Laboratory Celsum Technologies Ltd - Innovative, bespoke rheometry equipment & sensor supplies Infra Scientific Ltd - Manufacturer of novel, low viscosity equipment & UK distributor of Reologica Instruments AB rheometers

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For further information about Gammadot Rheology's testing & consultancy services, or if you have a specific problem / testing requirement which you would like Gammadot to provide a solution to, please contact us using the details at the top of the page or via the enquiry form HERE.

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